Stable anatase titanium dioxide and process for preparing the same

ABSTRACT

To hydrous titanium dioxide obtained by hydrolysis of titanium sulfate was added a predetermined amount of a water-soluble aluminum compound and/or a water-soluble zinc compound, the mixture is calcined, and a suitable amount of aluminum and/or zinc is introduced into the crystals to make up the crystal defects of anatase-type titanium dioxide, so that it has increased stability and excellent color stability.

This application is the national phase under 35 U.S.C. §371 of prior PCTInternational Application No. PCT/JP96/03843 which has an Internationalfiling date of Dec. 27, 1996 which designated the United States ofAmerica, the entire contents of which are hereby incorporated byreference.

TECHNICAL FIELD

The present invention relates to anatase-type titanium dioxide, moreparticularly to titanium dioxide powder which is bluish and has highwhiteness, containing in its crystals minute amounts of aluminum and/orzinc, so that it does not discolor upon high-temperature treatment, isexcellent in resistance to light and in weatherability, and has highchemical stability as well as relates to a manufacturing method formanufacturing the same.

BACKGROUND ART

Titanium dioxide is used widely as a white pigment and the like.Titanium dioxide includes two crystallographic systems, i.e.,anatase-type one which is of a low-temperature stable phase andrutile-type one which is of a high-temperature stable phase. When usedas a pigment, there is made a good use of them according to theircharacteristics. For example, anatase-type titanium dioxide ischaracterized in that it is bluish in color tone as compared with therutile-type one.

Hitherto, anatase-type titanium dioxide has been manufactured by asulfuric acid method on an industrial scale. This manufacturing methodis usually performed by hydrolyzing an aqueous titanyl sulfate solutionto produce hydrous titanium dioxide slurry, calcinating the slurry at850 to 1100° C. to obtain anatase-type titanium dioxide powder having apredetermined particle size.

Such conventional anatase-type titanium dioxide has a problem in that ascompared with rutile-type titanium dioxide, it tends to be discolored sothat it has low light resistance and low weatherability. Morespecifically, generally titanium dioxide crystals have more or lesspartial structural defects and an increase in the structural defectsreduces their chemical stability so that when they are used as apigment, they tend to be discolored due to external energy such asultraviolet rays, heat, grinding force or the like. The anatase-typetitanium dioxide manufactured by the conventional sulfuric acid methodhas more crystal defects and hence tends to be discolored thanrutile-type titanium dioxide. In particular, when titanium dioxide isused as a colorant for plastics, it is a recent trend to use higherkneading temperatures; sometimes the treatment temperature may exceed300° C. The conventional anatase-type titanium dioxide suffersconsiderable discoloration at treatment temperatures of 300° C. orhigher, thus deteriorating the color tone of the plastics.

The present invention is to solve the above-mentioned problemsassociated with the conventional anatase-type titanium dioxide and hasfor its object to provide anatase-type titanium dioxide which has a highdegree of whiteness, being difficult to discolor by high-temperaturetreatments, and has good chemical stability with excellent lightresistance and weatherability and to provide a manufacturing methodtherefor. In the following explanation, sometimes, the state of having ahigh degree of whiteness, being difficult to discolor by hightemperature treatments, and having good chemical stability withexcellent light resistance and weatherability is referred to as havinghigh color stability for convenience's sake.

DISCLOSURE OF THE INVENTION

The anatase-type titanium dioxide of the present invention ischaracterized by (1) comprising in titanium dioxide crystals divalent ortrivalent non-colored cations whose hexadentate ion radius is between0.6 Å or more and 0.9 Å or less, whereby more increased color stabilityis obtained. As the preferred non-colored cations, (2) at least one ofeither aluminum or zinc is introduced into the crystal.

The contents of aluminum and zinc introduced into the crystal aresuitably (3) 0.02 to 0.4% of aluminum, preferably 0.04 to 0.3% ofaluminum, and (4) 0.05 to 1.0% of zinc, preferably 0.1 to 0.6% of zinc,and when the both are used in combination, (5) the sum of the both is0.02 to 1.0%, preferably 0.04 to 0.6%, and the content of aluminum is0.4% or less. (6) It is suitable that the titanium dioxide has anaverage particle diameter of primary particles of 0.01 to 1.0 μm.

Further, the present invention provides (7) a method for manufacturingtitanium dioxide characterized by comprising adding an aluminum compoundand/or a zinc compound to hydrous titanium dioxide obtained byhydrolysis of titanium sulfate and calcinating the mixture to formanatase-type titanium dioxide which contains aluminum and/or zinc in thecrystal thereof. (8) By this method can be obtained anatase-typetitanium dioxide having high color stability, which contains 0.02 to0.4% of aluminum, 0.05 to 1.0% of zinc, or both aluminum and zinc withthe sum of the both being 0.02 to 1.0% with the content of aluminumbeing 0.4% or less in the crystal thereof.

The above-mentioned manufacturing method of the present inventionincludes (9) a method comprising dissolving a water-soluble aluminumcompound and/or a water-soluble zinc compound in a slurry of hydroustitanium dioxide, drying the slurry, and then calcinating at 850 to1100° C., and (10) a method comprising mixing aluminum compound powderand/or zinc compound powder with titanium dioxide powder obtained bydrying the slurry of hydrous titanium dioxide, and calcinating themixture at 850 to 1100° C.

BEST MODE FOR CARRYING OUT THE INVENTION

(I) Titanium Dioxide of the Present Invention

Titanium dioxide crystals have a structure in which six oxygen ions arecoordinated to one titanium ion and hence anatase-type crystals arestronger in covalent bonding than rutile-type crystals, which are ionic.The present invention is to increase the color stability of theanatase-type titanium dioxide.

It is assumed that from the crystallographic viewpoint, thediscoloration of titanium dioxide is attributable mainly to theincorporation of free electrons generated by crystal defects intotetravalent titanium ions to convert them trivalent titanium (violetcolor). In order to capture the free electrons, divalent or trivalentmetal ions may be doped to titanium dioxide to generate holes; thedopant ions are required to have an ionic radius, which is close to theionic radius of the tetravalent titanium ion (Ti⁴⁴⁺ : 0.75 Å), and to beselected from non-colored ions in order not to deteriorate the whitenessof titanium dioxide as far as possible.

Since the crystal of titanium dioxide is constituted by hexacoordinatetitanium ions (Ti⁴⁺), the titanium dioxide of the present invention isanatase-type titanium dioxide which has an ionic radius of 0.6 Å to 0.9Å, which is close to that of hexacoordinate titanium ion (Ti⁴⁺), andwhich has increased color stability by incorporation of divalent ortrivalent non-colored ions in the titanium dioxide crystal. Note thatthe above-mentioned ionic radii are values obtained by taking the radiiof O²⁻ and F⁻ as 1.26 Å and 1.19 Å, respectively, and based thereon.According to Table 15.23 at page II-717 of "KAGAKU BINRAN KISO-HEN"(Handbook of Chemistry for Basic), the 3rd Ed., those ions which haveionic radii close to the ionic radius of tetravalent titanium ioninclude the following ions (the values in the parentheses are of ionicradii of hexadentate ions).

Fe³⁺ (0.69 Å), Co³⁺ (0.69 to 0.75 Å), Ni²⁺ (0.70 to 0.74 Å), Cu²⁺ (0.87Å), Al³⁺ (0.68 Å), Zn²⁺ (0.88 Å), Ga³⁺ (0.76 Å), Mg²⁺ (0.86 Å)

Of these, Fe³⁺, Co³⁺, Ni²⁺, and Cu²⁺ are not preferred since they arecolored ions. For the purposes of the present invention are suited Al³⁺,Zn²⁺, Ga³⁺, and Mg²⁺. Of these, Al³⁺ and Zn²⁺ are preferred from theviewpoints of effects and economy.

In a preferred embodiment of the present invention, at least one ofeither aluminum ion or zinc ion is incorporated into titanium dioxidecrystal. This makes up crystal defects and increases stability, so thatthere can be obtained powder, which is difficult to be discolored athigh temperatures, has excellent light resistance and weatherability andis strongly bluish and has high brightness.

The amount of aluminum and/or zinc to be incorporated into the crystalis suitably 0.02 to 0.4% as aluminum ion, preferably 0.04 to 0.3% asaluminum ion and/or 0.05 to 1.0% of zinc ion, preferably 0.1 to 0.6% ofzinc ion. When aluminum and zinc are used in combination, a suitablerange is such that the sum of the amounts of their ions is 0.02 to 1.0%,preferably 0.04 to 0.6% and the amount of aluminum is 0.4% or less.

If the incorporation amount of aluminum or zinc is smaller than theabove-mentioned range, there will be obtained only insufficient effectsfor increasing the chemical stability of titanium dioxide. On the otherhand, if the incorporation is larger than the above-mentioned range,free aluminum or zinc in the form of oxides will coexist as mixed withthe titanium dioxide particles so that the pigment performances such asopacifying force and brightness are decreased.

Further, the upper limit of the amount of aluminum to be doped is abouthalf that of the doping amount of zinc. This is because, in case ofexceeding the additional amounts of aluminum, the particles tend to formhard mass and the dispersibility required for pigments is deteriorated.Zinc has a less tendency toward such.

In addition to those incorporated in the inside of the crystals, somealuminum and zinc are attached to the surface of the particles. Thealuminum content and zinc content referred herein relate to the amountsof them incorporated into the inside of the titanium dioxide crystalsbut do not include the amounts of those attached to the surface of theparticles.

Anatase-type titanium dioxides manufactured on an industrial scaleinclude one which contains about 0.01% of aluminum inclusive of thatderived from raw material ores or that contaminating during themanufacturing process. However, this amount is not effective inincreasing chemical stability (color stability).

Next, the anatase-type titanium dioxide of the present invention hassuitably an average particle diameter of 0.01 to 1.0 μm for primaryparticles. If the average particle diameter of primary particles isbelow 0.01 μm, the ratio of the surface area that are high in freeenergy to the total surface area of the particles will increase, causingthe particles chemically unstable. On the other hand, the averageparticle diameter exceeding 1.0 μm is undesirable since basic physicalproperties required for pigments cannot be maintained. In order toobtain titanium dioxide particles having an average particle diameter ofprimary particles within the above-described range, there may beperformed in the manufacturing method described hereinbelow adjustmentof conditions of precipitation upon hydrolysis of titanyl sulfate,adjustment of temperature in the subsequent calcination step or the likeadjustment.

(II) Manufacturing Method of the Present Invention

The anatase-type titanium dioxide of the present invention can bemanufactured by a sulfuric acid method, in which an aluminum compoundand/or a zinc compound in amounts depending on their incorporationamounts (doping amounts) are/is added to the hydrous titanium dioxideobtained by hydrolysis of titanium sulfate and the mixture is calcined.

In the manufacturing method of anatase-type titanium dioxide by aconventional sulfuric acid method, the aqueous titanium sulfate solutionobtained by dissolving ores such as ilmenite and titanium slag insulfuric acid is hydrolyzed to form a slurry of hydrous titaniumdioxide, which then is rinsed and dried, and calcined at 850 to 1100° C.to obtain anatase-type titanium dioxide powder.

In the manufacturing method of the present invention, the hydroustitanium dioxide is rinsed and after adjusting the concentration oftitanium dioxide in the suspension, an aluminum compound and/or a zinccompound in amounts corresponding to the respective introduction amountsare/is added, and the mixed slurry was calcined after drying.

As the aluminum compound and zinc compound, water-soluble compounds maybe added in a wet process or powdery compounds may be added in a dryprocess. As the water-soluble aluminum compound, there may be usedaluminum sulfate and the like, while as the powdery aluminum compound,there may be used alumina and the like. Further, as the water-solublezinc compound, there may be used zinc sulfate and the like, and as thepowdery zinc compound, there may be used zinc oxide and the like.

When the addition is made by a wet process, a predetermined amount ofaluminum sulfate, zinc sulfate or the like is dissolved in theabove-mentioned slurry of hydrous titanium dioxide, and then theresulting slurry is dried and calcined. The addition by a dry processmay be carried out by drying the above-mentioned slurry of hydroustitanium dioxide into powder, mixing it with a predetermined amount ofalumina powder and/or zinc oxide powder, and stirring it to disperseuniformly.

In either of the wet or dry manufacturing methods, it is not the casethat the total amount of the aluminum or zinc contained in the aluminumcompound or the zinc compound added to the titanium dioxide isincorporated into the crystal but the yield of incorporation varieswidely depending on the method of addition or mixing as well ascalcination and hence it is preferred that the amount of addition bedetermined depending on these conditions.

In addition to the above, in the manufacturing method for manufacturinganatase-type titanium dioxide on an industrial scale, small amounts ofpotassium and a phosphorus compound are added before calcination inorder to control the particle size and hardness thereof and further toinhibit the production of rutile-type crystals. If the addition of theseis omitted, the particle size and hardness will be non-uniform,resulting in loss of the features as a pigment. More specifically,potassium controls the fusion of particles during calcination to reducefluctuation in particle size. Usually, as the potassium source is usedpotassium carbonate, which is added in amounts of about 0.2 to 0.5% aspotassium carbonate. Phosphorus inhibits the conversion into rutile.Usually, as the source of phosphorus are used ammonium primary,secondary and/or tertiary phosphates, which are added in amounts ofabout 0.05 to 0.2% as diphosphorus pentaoxide. Instead of potassiumcarbonate and ammonium primary, secondary and/or tertiary phosphate,there may be added tripotassium phosphate and potassium carbonate. Notethat the potassium is washed off in a wet finishing step aftercalcination.

The slurry or mixed powder of raw materials is calcined at 850 to 1,100°C. If the calcination temperature is below 850° C., the calcination willbe performed only insufficiently. On the other hand, if it is above1,100° C., the brightness and dispersibility required for pigments willbe deteriorated considerably because of sintering occurrence in theparticles. Calcination at a relatively low temperature for a long periodof time rather than that at a high temperature for a short period oftime will yield a less amount of sintering to give rise to powder withgood dispersibility.

By the above-described manufacturing method, there can be obtainedanatase-type titanium dioxide powder which has chemical stability andexcellent light resistance.

(III) EXAMPLES

Examples of the present invention are described below. They are onlyexemplary and shall in no way be construed as limiting the scope of thepresent invention. In the following examples, the amounts of aluminumand zinc contained in titanium dioxide were measured in the methodsdescribed below. The particle diameter was determined by measuring thesize of primary particles using transmission-type electron microscopeand calculating an average diameter therefrom on a weight basis.

(1) Aluminum Content and Zinc Content on the Surface of Particles

1 g of titanium dioxide particles was mixed with 100 g of 5%hydrochloric acid and extracted with heating and the concentrations ofaluminum and of zinc in the extract solution were determined by ICP orthe like.

(2) Aluminum Content and Zinc Content Inside the Crystals

To 10 to 15 ml of concentrated sulfuric acid was added 5 ml ofconcentrated nitric acid. To the mixture was added 1 g of titaniumdioxide and the mixture was heated and optionally hydrofluoric acid wasadded if desired to dissolve titanium dioxide. The concentrations ofaluminum and of zinc in the resulting solution were determined by ICP orthe like. From the amounts obtained were subtracted the amounts of thealuminum and zinc on the surface of the particles to obtain the contentsof aluminum and of zinc contained inside the crystals.

Example 1

Based on the manufacturing method for manufacturing titanium dioxide bya general sulfuric acid method, titanium sulfate was hydrolyzed toobtain hydrous titanium dioxide slurry. After filtration and drying, theslurry was converted to an aqueous dispersion with a titanium dioxideconcentration of 33%. To 1,000 g (330 g in terms of TiO₂) of thesuspension were added 1.3 g of potassium carbonate, 0.7 g of diammoniumphosphate, and 0.33 g of aluminum sulfate as aluminum (Al additionratio:0.10%). After drying, the mixed slurry thus obtained was left tostand in a heating furnace at 800° C. for 1 hour and calcined at 960° C.for 3 hours, and then pulverized to obtain titanium dioxide powder withan average particle diameter of primary particles of 0.20 μm.

The powder was confirmed to be anatase-type titanium dioxide by X-raydiffraction. Further, measurement of the aluminum content of thetitanium dioxide powder indicated that the amount of aluminum of thetotal particle was 0.12%, with the amount of aluminum on the surfacebeing 0.01% and therefore the amount of aluminum contained inside thecrystal being 0.11%.

Example 2

Titanium dioxide powder was manufactured under the same conditions as inExample 1 except that the amount of aluminum sulfate added was changedto 1.0% as aluminum (Al addition ratio:0.30%). The total amount ofaluminum in the titanium dioxide was 0.31%, with the amount of aluminumon the surface being 0.02% and therefore the amount of aluminumcontained inside the crystal being 0.29%. The primary particles had anaverage particle diameter of 0.23 μm.

Example 3

To 440 g (330 g in terms of TiO₂) of powder (TiO₂ concentration:75%)obtained by drying the hydrous titanium dioxide slurry used in Example 1were added 1.3 g of potassium carbonate, 0.7 g of diammonium phosphate,and 0.33 g of alumina powder as aluminum (Al addition ratio:0.10%). Themixture thus obtained was left to stand in a heating furnace at 800° C.for 1 hour, calcined at 960° C. for 3 hours, and then pulverized toobtain anatase-type titanium dioxide powder with an average particlediameter of primary particles of 0.20 μm. Measurement of the aluminumcontent of the titanium dioxide powder in the same manner as in Example1 indicated that the amount of aluminum of the total particle was 0.11%,with the amount of aluminum on the surface being 0.04% and therefore theamount of aluminum contained inside the crystal being 0.07%.

Example 4

Titanium dioxide powder was manufactured under the same conditions as inExamples 1 except that the amount of aluminum sulfate added was changedto 0.165 g as aluminum (Al addition ratio:0.05%). The total amount ofaluminum in the titanium dioxide powder was 0.05%, with the amount ofaluminum on the surface being 0.01% and therefore the amount of aluminumcontained inside the crystal being 0.04%. The primary particles had anaverage particle diameter of 0.18 μm.

Example 5

Based on the manufacturing method for manufacturing titanium dioxide bya general sulfuric acid method, titanium sulfate was hydrolyzed toobtain hydrous titanium dioxide slurry. After filtration and drying, theslurry was converted to an aqueous dispersion with a titanium dioxideconcentration of 33%. To 1000 g (330 g in terms of TiO₂) of thesuspension were added 1.3 g of potassium carbonate, 0.7 g of diammoniumphosphate, and 0.80 g of zinc sulfate as zinc (Zn addition ratio:0.10%).After drying, the mixed slurry thus obtained was left to stand in aheating furnace at 800° C. for 1 hour, calcined at 960° C. for 3 hours,and then pulverized to obtain titanium dioxide powder with an averageparticle diameter of primary particles of 0.20 μm.

Measurement of the zinc content of the titanium dioxide powder indicatedthat the amount of zinc of the total particle was 0.08%, with the amountof zinc on the surface being 0.01% and therefore the amount of zinccontained inside the crystal being 0.07%. The above-described titaniumdioxide powder was confirmed to be of anatase-type by X-ray diffraction.

Example 6

Titanium dioxide powder was manufactured under the same conditions as inExamples 5 except that the amount of zinc sulfate added was changed to2.40 g as zinc (Zn addition ratio:0.30%). The total amount of zinc inthe titanium dioxide powder was 0.29%, with the amount of zinc on thesurface being 0.13% and therefore the amount of zinc contained insidethe crystal being 0.16%. The primary particles had an average particlediameter of 0.23 μm.

Example 7

To 440 g (330 g in terms of TiO₂) of powder (TiO₂ concentration:75%)obtained by drying the hydrous titanium dioxide slurry used in Example 1were added 1.3 g of potassium carbonate, 0.7 g of diammonium phosphate,and 0.80 g of zinc oxide powder as zinc (Zn addition ratio:0.10%). Themixture thus obtained was left to stand in a heating furnace at 800° C.for 1 hour, calcined at 960° C. for 3 hours, and then pulverized toobtain anatase-type titanium dioxide powder with an average particlediameter of primary particles of 0.20 μm.

Measurement of the aluminum content of the titanium dioxide powder inthe same manner as in Example 1 indicated that the amount of zinc of thetotal particle was 0.20%, with the amount of zinc on the surface being0.12% and therefore the amount of zinc contained inside the crystalbeing 0.08%.

Example 8

Titanium dioxide powder was manufactured under the same conditions as inExamples 1 except that the amount of zinc sulfate added was changed to8.0 g as zinc (Zn addition ratio:1.0%). The total amount of zinc in thetitanium dioxide powder was 0.95%, with the amount of zinc on thesurface being 0.38% and therefore the amount of zinc contained insidethe crystal being 0.57%. The primary particles had an average particlediameter of 0.18 μm.

Examples 9˜12

Titanium dioxide powder was manufactured under the same conditions as inExample 1 except that aluminum sulfate was replaced by a mixture ofaluminum sulfate and zinc sulfate in each example. The amounts ofaluminum and zinc contained inside the crystals were measured and theresults obtained are shown in Table 1.

Comparative Examples 1˜4

Anatase-type titanium dioxide powder was manufactured in the same manneras in Example 1 except that no aluminum sulfated was added (ComparativeExample No. 4). Further, anatase-type titanium dioxide powder wasmanufactured in the same manner as in Example 1 except that the contentsof aluminum and/or of zinc were changed as shown in Table 1 (ComparativeExamples Nos. 1 to 3).

Method for Evaluating Light Stability

After adding 2 g each of titanium dioxide powder in above-mentionedexamples and comparative samples to 1.6 ml of a water-solublemethylolmelamine resin paint and kneading, the mixture was coated on aglass plate with an applicator (4 mil) and dried. The plate was exposedwith ultraviolet rays for 8 hours (ultraviolet lamp: SHL-1000UVQ-2manufactured by TOSHIBA CORPORATION) while rotating the plate on aplane. The color difference of the glass plate was measured before andafter the exposure with ultraviolet rays and obtained. For themeasurements, a color difference meter as prescribed by JIS-Z-8722(Color Computer Model SM-5 manufactured by SUGA SHIKENKI CO., LTD.) wasused and the color difference was indicated according to the Huntercolor-difference equation as prescribed by JIS-Z-8730. The results areshown in Table 1.

Method for Evaluating Brightness

5 g each of the titanium dioxide powders in above-mentioned examples andcomparative samples was added to 45 g of polyethylene resin (MIRASON402, manufactured by MITSUI PETROCHEMICAL INDUSTRIES, LTD.) and afterkneading at 150° C. using a two-roll mill, the mixture was molded into 1mm thick sheet. The brightness of the sheet was measured using theabove-mentioned color difference meter. The results are presented inTable 1.

Method for Evaluating Thermal Stability

Polyethylene sheet containing the above-mentioned titanium dioxide washeated at 310° C. for 20 minutes in a small muffle furnace. The sheetwas measured using the above-described color difference meter. The colordifference between the sheets before and after heating was calculatedalong the Hunter color-difference equation prescribed by JIS-Z-8370. Theresults are indicated in Table 1.

As indicated by the results in Table 1, the comparative sample(Comparative Example No.4) corresponding to the conventional titaniumdioxide had a great tendency of being discolored since it had a colordifference of 2 or more in the light stability test and a colordifference of 7 or more in the thermal stability test. On the otherhand, the titanium dioxides of the present invention each had a highbrightness of 96 or more and a small color difference of 1.2 or less inthe light stability test and of 5.7 or less in the thermal stabilitytest, thus confirming that they are excellent in stabilities againstlight and heat.

Further, the samples with the doping amounts of aluminum and of zincbeing below the lower limit used in the present invention (ComparativeSamples Nos. 1 to 3) had color differences in light stability andthermal stability close to those of the conventional products, thusshowing less improvement effect. On the other hand, the samples with thedoping amounts above the upper limit used in the present invention(Comparative Samples Nos. 1 to 3) had each a reduced brightness.

                                      TABLE 1                                     __________________________________________________________________________                Al/Zn     Light    Thermal                                                    Amounts                                                                            Average                                                                            Stability                                                                              Stability                                                  inside                                                                             Particle                                                                           Color    Color                                          Manufactur- Crystal                                                                            Diameter                                                                           Difference                                                                         Bright-                                                                           Difference                                     ing method  (%)  (μm)                                                                            ΔE                                                                           ness                                                                              ΔE                                                                           Remarks                                   __________________________________________________________________________    Example 1                                                                           wet method                                                                          0.11 0.20 0.5  96.3                                                                              4.2  Al-doped                                  2     wet method                                                                          0.29 0.23 0.4  96.0                                                                              3.8                                            3     dry method                                                                          0.07 0.20 0.7  96.1                                                                              5.2                                            4     wet method                                                                          0.04 0.18 0.8  96.1                                                                              5.0                                            Example 5                                                                           wet method                                                                          0.07 0.20 1.2  96.1                                                                              5.7  Zn-doped                                  6     wet method                                                                          0.16 0.23 0.7  96.2                                                                              4.7                                            7     dry method                                                                          0.08 0.20 1.0  96.0                                                                              5.6                                            8     wet method                                                                          0.57 0.18 0.4  96.3                                                                              4.1                                            Example 9                                                                           wet method                                                                          Al: 0.02                                                                           0.21 1.1  96.3                                                                              5.3  Al + Zn-                                              Zn: 0.12                doped                                     10    wet method                                                                          Al: 0.19                                                                           0.21 0.6  96.1                                                                              4.4                                                        Zn: 0.09                                                          11    dry method                                                                          Al: 0.06                                                                           0.20 0.7  96.1                                                                              4.7                                                        Zn: 0.48                                                          12    wet method                                                                          Al: 0.28                                                                           0.23 0.3  96.0                                                                              3.2                                                        Zn: 0.51                                                          Comparative                                                                         wet method                                                                          0.01 0.19 1.9  96.0                                                                              7.3  Al-doped                                  Example 1   0.5  0.25 0.4  95.4                                                                              3.6                                            Comparative                                                                         wet method                                                                          0.01 0.18 1.8  96.0                                                                              8.4                                            Example 2   1.5  0.24 0.4  95.2                                                                              3.5                                            Comparative                                                                         wet method                                                                          0.01 0.19 1.9  96.1                                                                              8.6  Al + Zn-                                  Example 3   1.5  0.25 0.4  95.2                                                                              3.5  doped                                     Comparative                                                                         --    0    0.20 2.2  95.9                                                                              9.1                                            Example 4                                                                     __________________________________________________________________________

Industrial Applicability

The anatase-type titanium dioxide of the present invention has a higherbrightness as compared with the conventional ones and has highly bluishwhite color which is the most important requirement of anatase-typetitanium dioxide. Further, the anatase-type titanium dioxide of thepresent invention has optimal characteristics as a pigment in which ithas very high light resistance so that it is difficult to be discolored.In particular, when kneaded with plastics, its discoloration isinhibited largely at the time of high-temperature treatments as high asabout 300° C. Furthermore, according to the manufacturing method of thepresent invention, there is obtained the above-described titaniumdioxide powder having excellent light resistance with ease andeconomically.

What is claimed is:
 1. Anatase-type titanium dioxide compositioncomprising:a) titanium dioxide crystals doped with divalent or trivalentnon-colored metal cations; b) said cations having a hexadentate ionradius between 0.6 Å or more and 0.9 Å or less; c) said titanium dioxidecomposition having an average particle diameter of primary particles of0.01 to 1.0 μm; and d) said titanium dioxide composition exhibitingincreased color stability under high-temperature treatment as high asabout 300° C.
 2. The titanium dioxide composition as claimed in claim 1wherein said titanium dioxide composition contains at least one ofeither aluminum or zinc in the crystal.
 3. The titanium dioxidecomposition as claimed in claim 2 wherein said titanium dioxidecomposition contains 0.02 to 0.4% of aluminum.
 4. The titanium dioxidecomposition as claimed in claim 3 wherein said titanium dioxidecomposition contains 0.04 to 0.3% of aluminum.
 5. The titanium dioxidecomposition as claimed in claim 2 wherein said titanium dioxidecomposition contains 0.05 to 1.0% of zinc.
 6. The titanium dioxidecomposition as claimed in claim 5 wherein said titanium dioxidecomposition contains 0.1 to 1.0% of zinc.
 7. The titanium dioxidecomposition as claimed in claim 2 wherein said titanium dioxidecomposition contains both aluminum and zinc, and wherein the sum of bothis 0.05 to 1.0% and the content of aluminum is 0.4% or less.
 8. Thetitanium dioxide composition as claimed in claim 7 wherein said titaniumdioxide composition contains both aluminum and zinc, and wherein the sumof both is 0.04 to 0.6% and the content of aluminum is 0.4% or less. 9.A method for manufacturing an anatase-type titanium dioxide composition,comprising:a) adding an aluminum compound, a zinc compound or mixturesthereof to hydrous titanium dioxide obtained by hydrolysis of titaniumsulfate; and b) calcinating the mixture to form an anatase-type titaniumdioxide composition with increased color stability underhigh-temperature treatments as high as about 300° C. that containsaluminum, zinc or mixtures thereof in the crystal thereof.
 10. Themethod as claimed in claim 9, wherein said titanium dioxide compositioncontains 0.02 to 0.4% of aluminum or 0.05 to 1.0% of zinc in thecrystals thereof, or both aluminum and zinc with the sum of both being0.02 to 1.0% with the content of aluminum being 0.4% or less in thecrystal thereof.
 11. The method for the manufacturing an anatase-typetitanium dioxide composition with increased color stability underhigh-temperature treatment as high as about 300° C. as claimed in claims9 or 10 comprising:a) dissolving a water-soluble aluminum compound, awater soluble zinc compound or mixtures thereof in a slurry of hydroustitanium dioxide; b) drying the slurry; and then c) calcinating at 850to 1100° C.
 12. The method for the manufacturing an anatase-typetitanium dioxide composition with increased color stability underhigh-temperature treatment as high as about 300° C. as claimed in claims9 or 10 comprising:a) mixing aluminum compound, zinc compound ormixtures thereof with said titanium dioxide obtained by drying saidmixture of hydrous titanium dioxide; and b) calcinating the mixture at850 to 1100° C.